An electrical cable is an assembly of one or more wires running side by side or bundled, which is used as an electrical conductor, i.e., to carry electric current. One or more electrical cables and their corresponding connectors may be formed into a cable assembly,[1] which is not necessarily suitable for connecting two devices but can be a partial product (e.g. to be soldered onto a printed circuit board with a connector mounted to the housing). Cable assemblies can also take the form of a cable tree or cable harness, used to connect many terminals together.
Etymology
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The original meaning of cable in the electrical wiring sense was for submarine telegraph cables that were armoured with iron or steel wires. Early attempts to lay submarine cables without armouring failed because they were too easily damaged. The armouring in these early days (mid-19th century) was implemented in separate factories to the factories making the cable cores. These companies were specialists in manufacturing wire rope of the kind used for nautical cables. Hence, the finished armoured cores were also called cables. The term was later extended to any bundle of electrical conductors (or even a single conductor) enclosed in an outer sheath, whether or not it was armoured. The term is now also applied to telecommunications cables with fibre-optic cores within the outer sheath rather than copper conductors.
Uses
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6 inch (15 cm) outside diameter, oil-cooled cables, traversing the Grand Coulee Dam throughout. An example of a heavy cable for power transmission. Fire test in Sweden, showing fire rapidly spreading through the burning of cable insulation, a phenomenon of great importance for cables used in some installations. 500,000 circular mil (254 mm2) single conductor power cableElectrical cables are used to connect two or more devices, enabling the transfer of electrical signals or power from one device to the other. Long-distance communication takes place over undersea communication cables. Power cables are used for bulk transmission of alternating and direct current power, especially using high-voltage cable. Electrical cables are extensively used in building wiring for lighting, power and control circuits permanently installed in buildings. Since all the circuit conductors required can be installed in a cable at one time, installation labor is saved compared to certain other wiring methods.
Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual covering(s), assembly protection and protective covering(s). Electrical cables may be made more flexible by stranding the wires. In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Bunching small wires before concentric stranding adds the most flexibility. Copper wires in a cable may be bare, or they may be plated with a thin layer of another metal, most often tin but sometimes gold, silver or some other material. Tin, gold, and silver are much less prone to oxidation than copper, which may lengthen wire life, and makes soldering easier. Tinning is also used to provide lubrication between strands. Tinning was used to help removal of rubber insulation. Tight lays during stranding makes the cable extensible (CBA – as in telephone handset cords).[further explanation needed]
In the 19th century and early 20th century, electrical cable was often insulated using cloth, rubber or paper. Plastic materials are generally used today, except for high-reliability[clarification needed] power cables. The first thermoplastic used was gutta-percha (a natural latex) which was found useful for underwater cables in the 19th century. The first, and still very common, man-made plastic used for cable insulation was polyethylene. This was invented in 1930, but not available outside military use until after World War 2 during which a telegraph cable using it was laid across the English Channel to support troops following D-Day.[2]
Cables can be securely fastened and organized, such as by using trunking, cable trays, cable ties or cable lacing. Continuous-flex or flexible cables used in moving applications within cable carriers can be secured using strain relief devices or cable ties.
At high frequencies, current tends to run along the surface of the conductor. This is known as the skin effect.
Characteristics
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Any current-carrying conductor, including a cable, radiates an electromagnetic field. Likewise, any conductor or cable will pick up energy from any existing electromagnetic field around it. These effects are often undesirable, in the first case amounting to unwanted transmission of energy which may adversely affect nearby equipment or other parts of the same piece of equipment; and in the second case, unwanted pickup of noise which may mask the desired signal being carried by the cable, or, if the cable is carrying power supply or control voltages, pollute them to such an extent as to cause equipment malfunction.
The first solution to these problems is to keep cable lengths in buildings short since pick up and transmission are essentially proportional to the length of the cable. The second solution is to route cables away from trouble. Beyond this, there are particular cable designs that minimize electromagnetic pickup and transmission. Three of the principal design techniques are shielding, coaxial geometry, and twisted-pair geometry.
Shielding makes use of the electrical principle of the Faraday cage. The cable is encased for its entire length in foil or wire mesh. All wires running inside this shielding layer will be to a large extent decoupled from external electrical fields, particularly if the shield is connected to a point of constant voltage, such as earth or ground. Simple shielding of this type is not greatly effective against low-frequency magnetic fields, however - such as magnetic "hum" from a nearby power transformer. A grounded shield on cables operating at 2.5 kV or more gathers leakage current and capacitive current, protecting people from electric shock and equalizing stress on the cable insulation.
Coaxial design helps to further reduce low-frequency magnetic transmission and pickup. In this design the foil or mesh shield has a circular cross section and the inner conductor is exactly at its center. This causes the voltages induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel each other.
A twisted pair has two wires of a cable twisted around each other. This can be demonstrated by putting one end of a pair of wires in a hand drill and turning while maintaining moderate tension on the line. Where the interfering signal has a wavelength that is long compared to the pitch of the twisted pair, alternate lengths of wires develop opposing voltages, tending to cancel the effect of the interference.
Fire protection
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Electrical cable jacket material is usually constructed of flexible plastic which will burn. The fire hazard of grouped cables can be significant.[3] Cables jacketing materials can be formulated to prevent fire spread[4] (see Mineral-insulated copper-clad cable). Alternately, fire spread amongst combustible cables can be prevented by the application of fire retardant coatings directly on the cable exterior,[5] or the fire threat can be isolated by the installation of boxes constructed of noncombustible materials around the bulk cable installation.
Types
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A 250 V, 16 A electrical cable on a reelCENELEC HD 361 is a ratified standard published by CENELEC, which relates to wire and cable marking type, whose goal is to harmonize cables. Deutsches Institut für Normung (DIN, VDE) has released a similar standard (DIN VDE 0292).
Hybrid cables
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Hybrid optical and electrical cables can be used in wireless outdoor fiber-to-the-antenna (FTTA) applications. In these cables, the optical fibers carry information, and the electrical conductors are used to transmit power. These cables can be placed in several environments to serve antennas mounted on poles, towers or other structures. Local safety regulations may apply.
See also
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References
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Further reading
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The invention of the underground power cable was a ground breaking and innovative creation that birthed our every day lives into a new world of light forever.
Thomas Edison was born on the 11th of February in the year 1847, residing for a short time in Milan, Ohio of the United States of America. For most of his life in education, Thomas was home schooled by his mother, this came as a result of one of Edisons teachers referring to the young boy as “Addled” in his first years of schooling.
“My mother was the making of me. She was so true, so sure of me, and I felt I had someone to live for, someone I must not disappoint.”
At a very early age, Edison always showed interest and fascination in the areas of mechanics and chemical experiments, but by the age of twelve he had lost almost all hearing – it has never been reported why this happened. As Edison got older he dabbled in many different areas of work. In the winter of 1862, Edison took work as a telegraph operator after being rewarded with the relevant training after saving a mans 3-year-old son from a boxcar track. From there and onward, Edison traveled from city to city searching for available jobs within the telegraph industry.
In the year of 1869, Edison took it upon himself to devote all of his time and energy into his inventions and experiments, resigning from his job at the Western Unions Office. That same year, he invented the ‘electric vote recorder’, and received his first patent for the device. This invention was not successful, resulting in Edison heading back to work within the telegraph industry. This time, he tried his luck within mechanical engineering and repairs.
1878 came along and Edison focused on the field of electricity and lighting, leaving his other inventions behind. On October 15 of that year, the Edison Electric Light Co was formed by Edison himself and a group of investors. The goal of the company was to provide financial support for Edisons electrical lighting experiments, manage any resulting patents from his inventions, and work on developing an electric light system that could inevitably light up an entire city. After Edison handed over his patents for the company that year, he received a large share of stock in return.
Every attempt and every failure was Edisons self assuring proof that he was one step closer to lighting up the community of Menlo Park in New Jersey. As lamps were installed into the park laboratory, many people ventured to the community to see the newest innovative invention. In 1880, on the day of the Presidential Election, Thomas Edison had insulated, set and prepared his Menlo Park lamp setting which was only to be trialed if James A. Garfield won the election. When the results came through as a win for Garfield, Edison gave the OK to light up his lamps. The row of insulated jute lit up the park, marking the night of Garfield’s Presidential election as a success.
“Edison didn’t just develop a lamp; he invented a whole system of creating and delivering electricity.”
In 1882, Edison shifted his knowledge to the state of New York. To prove that his invention could successfully work, the first commercial electric lighting system was installed on Pearl Street, along the financial district of Lower Manhattan which was bordering City Hall and two newspaper factories.
Only around four hundred lamps were lit in the beginning of Edisons successful invention being produced, and within a year, over five hundred customers were using up to ten and a half thousand lamps. After his small taste of success with the electrical lamps, Edison formed several of his own companies so that he could start vastly manufacturing and operating the equipment that was needed for the new lighting system. His lighting system was also taken to the Paris Lighting Exposition in 1881, the Crystal Palace in London in 1882, and the coronation of the czar in Moscow. The great exposure of Edisons invention led to the establishment of many companies which expanded across several European countries. There was the Edison Electric Illuminating Company of New York, the Edison Electric Tube Company, the Edison Lamp Works, and the Edison Machine Works.
In todays world, lights are a necessity. We need lights to work, cook, clean, and read. Lights are also used to save the lives of missing people, to search for lost aircraft’s, to create warmth in the winter, to quickly microwave our meals, and to spend time with family and friends during the evenings. There is not a day, or night, that goes by where lights are not in use. Thanks to the mind of Thomas Edison, man has been able to mass produce incredible things with light, accompanying us all in progressing into the future one electrical cable at a time.
References:
The Raab Collection. (n.d.). Thomas Edison First Underground Wire | Raab Collection. [online] Available at: https://www.raabcollection.com/science-autographs/edison-first-underground-wire [Accessed 24 Jun. 2019].
The Library of Congress. (n.d.). Life of Thomas Alva Edison | Biography | Articles and Essays | Inventing Entertainment: The Early Motion Pictures and Sound Recordings of the Edison Companies | Digital Collections | Library of Congress. [online] Available at: https://www.loc.gov/collections/edison-company-motion-pictures-and-sound-recordings/articles-and-essays/biography/life-of-thomas-alva-edison/#N_3_ [Accessed 24 Jun. 2019].
Deziel, C. (2017). How Did Thomas Edison’s Light Bulb Work?. [online] Sciencing.com. Available at: https://sciencing.com/lightbulb-changed-over-years-5631574.html [Accessed 28 Jun. 2019].
Brown, M. (n.d.). Edison Patents Incandescent Lamp – This Day in Tech History. [online] This Day in Tech History. Available at: https://thisdayintechhistory.com/01/27/edison-patents-incandescent-lamp/ [Accessed 28 Jun. 2019].
Oatman-Stanford, H. (2015). Let There Be Light Bulbs: How Incandescents Became the Icons of Innovation | Collectors Weekly. [online] Collectorsweekly.com. Available at: https://www.collectorsweekly.com/articles/let-there-be-light-bulbs/ [Accessed 28 Jun. 2019].